1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus and a method for diagnosing a DAC amplifier unit in the charged particle beam writing apparatus.
2. Background Art
In a process for manufacturing semiconductor devices, a reticle is used to form a fine circuit pattern. It is known that an electron beam writing apparatus, one of charged particle beam writing apparatuses, is used to form a pattern in a reticle.
In recent years, to achieve higher integration of the semiconductor devices, the pattern of the reticle has been finer and finer and the number of shots per reticle has increased to tera-level shots per reticle. With the increased number of shots per reticle, the amount of entire shot data increases. In addition, it is requested to improve a writing throughput and thus a data transfer rate between a deflection control circuit and a digital-to-analog converter (DAC) amplifier unit is increased. Also, the DAC amplifier unit has a higher processing rate.
The DAC amplifier unit has a digital section that outputs digital data received from the deflection control circuit to a digital-to-analog converter (DAC). With the above-mentioned increase in the data transfer rate and processing rate, the digital data input to the digital section is switched at high speed. As a result, an error may easily occur in the digital section included in the DAC amplifier unit. If an error occurs in the DAC amplifier unit, then the reticle will be defective. For that reason, it is necessary to diagnose the operation of the DAC amplifier unit.
Conventionally known methods for diagnosing a DAC amplifier unit include a linearity test using a digital multimeter. In the linearity test, analog data converted from digital data by a DAC is input to the digital multimeter at a rate lower than an actual writing rate. The digital multimeter then converts the analog data into digital data. The digital data converted by the digital multimeter is compared with the original digital data to diagnose static characteristics of the DAC amplifier unit.
Errors in the digital section accompanied by the aforementioned increased rates cannot be found based on only diagnosis of the static characteristics of the DAC amplifier unit, which means that the DAC amplifier unit is not sufficiently diagnosed. Thus, the need to diagnose dynamic characteristics of the DAC amplifier unit increases. Since when a failure occurs in the DAC amplifier unit it is difficult to specify the location of the failure, the electron beam writing apparatus will disadvantageously remain down for a long period of time.
An apparatus for maintaining and controlling the electron beam writing apparatus as to whether it is in normal operation or not is known in the art (refer to Japanese Patent Laid-open No. 2007-324229, for example). An apparatus described in Japanese Patent Laid-open No. 2007-324229 has a write circuit. The write circuit receives predetermined layout information and a writing condition. As a result, the write circuit outputs write processing data. The apparatus collects the write processing data and compares the write processing data with correct data to diagnose the write circuit. Japanese Patent Laid-open No. 2007-324229, however, does not describe diagnosis of dynamic characteristics of the DAC amplifier unit.
The present invention has been devised to solve the aforementioned problem. It is, therefore, an object of the present invention to provide a charged particle beam writing apparatus capable of diagnosing dynamic characteristics of a DAC amplifier unit and a method for diagnosing the DAC amplifier unit in the charged particle beam writing apparatus.